Given the talent involved — producer Tom Hanks, director Gil Kenan (Monster House), screenwriter Caroline Thompson (Edward Scissorhands) — City of Ember should simply be better than the merely good-enough dystopian kids movie that it is. Especially because the elusive Bill Murray pops up, playing the pot-bellied mayor of a dying underground city. He’s fun, and the movie, slathered with grimy color, looks striking (think The City of Lost Children for, well, children). But the story, which follows two kids who try to save their burg from blackouts, isn’t well-executed, losing itself to unclear mythology and sci-fi gibberish. B?